1. Field of the Invention
This invention relates to integrated circuit packages mainly for flip-chip mounting.
2. Description of the Related Art
As conventional integrated circuit packages for flip-chip bonding, there are a type in which a grounded metallic film 103 exists right under an integrated circuit chip 101 to be flip-chip mounted onto a dielectric substrate 102 as shown in FIGS. 13A and 13B, or a type in which a surface of the dielectric substrate 102 is unprotected right under the integrated circuit chip 101 as shown in FIGS. 14A and 14B. FIG. 13B and FIG. 14B are sectional views showing the structures taken along the Ixe2x80x94I line in FIG. 13A and the IIxe2x80x94II line in FIG. 14A, respectively.
These integrated circuit packages are structured to be provided with the grounded metallic film 103 on the dielectric substrate 102, lead-out wirings 104, 105 for leading out a high frequency signal to the outside, power supply wirings 106 to 109 and a pad 111 for connecting with a projecting metal 110 which is provided on the integrated circuit chip 101 for flip-chip mounting, as shown in FIG. 13 and FIG. 14.
Moreover, the thickness of the dielectric substrate 102 can be freely decided in the conventional integrated circuit package.
The integrated circuit package generally has a disadvantage that an unnecessary electromagnetic wave is generated and emitted at a surface of a circuit of the integrated circuit chip or parts such as a bump or a pillar for connecting the circuit and a wiring on the dielectric substrate. This is because an electric field laid between a signal line and a grounding conductor is forced to change at a discontinuous part, thereby causing a different transmission mode to occur.
The electromagnetic wave which is emitted to a gap is reflected by the grounded metallic film right under the chip or the unprotected surface of the dielectric substrate to enter into the various parts of a circuit pattern, which causes a problem that the operation of the circuit becomes unstable.
It is an object of the present invention to provide an integrated circuit package which absorbs an unnecessary electromagnetic wave emitted from an integrated circuit of an integrated circuit chip with extremely high efficiency and realizes stabilization of the operation of a circuit.
According to the first aspect of the present invention, an integrated circuit package with a dielectric substrate provided with a grounding conductor on its rear surface and an electric-electronic circuit of a patterned metallic film on its upper surface respectively and an integrated circuit chip being connected to oppose to each other, comprises an electric resistance part being electrically independent of the metallic film on the dielectric substrate at an opposed position to the integrated circuit chip.
In this aspect, in addition to the provision of the electric resistance part, the thickness of the dielectric substrate is controlled in view of effectively absorbing the electromagnetic wave.
More specifically, it is preferable to control the thickness to be almost a quarter of a desired signal wavelength to be absorbed, for example, the signal wavelength which is decided by a frequency used in the integrated circuit of the integrated circuit chip and the specific inductive capacity of the dielectric substrate, or to be within the range of one-eighth to one-half the signal wavelength.
Further, in consideration of absorbing signal wavelengths in a wide range or those within a predetermined range, it is preferable to process the opposed position of the dielectric substrate to be in a recessed and protruding shape. In this case, the electromagnetic waves within the predetermined range can be absorbed by continuously changing the thickness of the dielectric substrate, and the electromagnetic waves having predetermined wavelengths can be absorbed by discontinuously changing the same.
Moreover, in consideration of precisely and properly absorbing the electromagnetic wave, in this aspect, the electric resistance part is controlled to have a surface resistance value which is almost equal to the characteristic impedance between the electric resistance part and the dielectric substrate.
More specifically, when a gap is formed between the electric resistance part and the dielectric substrate, the surface resistance value is controlled to be equal to the characteristic impedance of air in the gap. It is also suitable to fill the gap with a predetermined dielectric substance in order to control the surface resistance value easily.
Further, in this aspect, in consideration of enhancing grounding of the integrated circuit of the integrated circuit chip, an insulation film is provided on the electric resistance part and a metallic conductor in the form of a mesh is provided thereon for electrically connecting with the integrated circuit.
Furthermore, in this aspect, in addition to the formation of the electric resistance part as a resistance film, it is suitable to form the electric resistance part by filling a groove with a resistance material which is formed at the opposed position on the dielectric substrate.
According to the second aspect of the present invention, an integrated circuit package similar to that in the first aspect, comprises an electric resistance part being electrically independent of a metallic film on a dielectric substrate at an opposed position to an integrated circuit chip, and the thickness of the dielectric substrate at the opposed position is specified so that a desired signal wavelength absorbed in the electric resistance part becomes an almost open end at a surface of the electric resistance part.
Also in this aspect, it is preferable to define the thickness of the dielectric substrate, change the thickness at the opposed position, regulate the surface resistance value of the electric resistance part and so on, similarly to that in the aforesaid first aspect.
In the integrated circuit package of the present invention, even when the electromagnetic wave of an unnecessary mode is generated, the electric resistance part which is provided on the dielectric substrate at the opposed position to the integrated circuit chip absorbs the electromagnetic wave without reflections in the opposed position. When the thickness of the grounded dielectric substrate is set to be one quarter of the signal wavelength which is decided by the frequency used in the integrated circuit and the specific inductive capacity of the dielectric substrate, a surface of the electric resistance part appears to be the electrically open end for the electromagnetic wave, so that an amplitude of a voltage due to the electromagnetic wave on the surface of the electric resistance part becomes maximum. Thereby, a current is generated on the surface of the electric resistance part because of the voltage by the electromagnetic wave, an energy loss is generated, and its value becomes maximum.
Further, the surface resistance value of the electric resistance part is made to coincide with the characteristic impedance decided by the relative permeability and the specific inductive capacity between a circuit pattern and the dielectric substrate, whereby a match between the characteristic impedance of the electromagnetic wave emitted to the gap and a characteristic impedance on the resistance film can be obtained and the energy is lost effectively.
Furthermore, when the thickness of the dielectric substrate is set to be within one-eighth to one-half the signal wavelength which is decided by the frequency used in the integrated circuit and the specific inductive capacity of the dielectric substance, it is possible to absorb the electromagnetic wave in a frequency range of a quarter of the signal wavelengths of the respective lengths.
According to the present invention, when the electric resistance part of a proper value is provided on the surface and a package substrate using the dielectric substrate of a proper thickness with its rear surface being grounded is used, the unnecessary electromagnetic wave which is emitted from the integrated circuit chip and the unnecessary electromagnetic wave which enters from the outside are removed with extremely high efficiency, which makes it possible to realize an integrated circuit module of high performance.